The present invention relates generally to electrical switching devices. More particularly, the present invention relates to electrical switching devices that have an architecture that facilitates access, maintenance, and repair to the device and reduces substation equipment and real estate.
A high voltage circuit breaker is a device used in the transmission and distribution of three phase electrical energy. When a sensor or protective relay detects a fault or other system disturbance on the protected circuit, the circuit breaker operates to physically separate current-carrying contacts in each of the three phases by opening the circuit to prevent the continued flow of current. In addition to its primary function of fault current interruption, a circuit breaker is capable of load current switching. A circuit switcher and load break switch are other types of switching device. As used herein, the expression xe2x80x9cswitching devicexe2x80x9d encompasses circuit breakers, circuit switches, dead tank breakers, live tank breakers, load break switches, reclosers, and any other type of electrical switch.
The major components of a circuit breaker or recloser include the interrupters, which function to open and close one or more sets of current carrying contacts housed therein; the operating mechanism, which provides the energy necessary to open or close the contacts; the arcing control mechanism and interrupting media, which interrupt current and create an open condition in the protected circuit; one or more tanks for housing the interrupters; and the bushings, which carry the high voltage electrical energy from the protected circuit into and out of the tank(s) (in a dead tank breaker). In addition, a mechanical linkage connects the interrupters and the operating mechanism.
Circuit breakers can differ in the overall configuration of these components. However, the operation of most circuit breakers is substantially the same. For example, a circuit breaker may include a single tank assembly which houses all of the interrupters. U.S. Pat. No. 4,442,329, Apr. 10, 1984, xe2x80x9cDead Tank Housing for High Voltage Circuit Breaker Employing Puffer Interrupters,xe2x80x9d discloses an example of the single tank configuration and is incorporated herein in its entirety by reference. Alternatively, a separate tank for each interrupter may be provided in a multiple tank configuration. An example of a prior art, multiple tank circuit breaker is depicted in FIGS. 1, 2, 3, and 4. Circuit breakers of this type can accommodate 72 kV, 145 kV, 242 kV, and 362 kV power sources.
The circuit breaker shown in FIG. 1 is commonly referred to as a xe2x80x9cdead tankxe2x80x9d because it is at ground potential. FIG. 1 provides a front view of a three phase or three-pole circuit breaker having three entrance bushing insulators, 10, 11, and 12, that correspond to each respective phase. The bushing insulators may be comprised of porcelain, composite, or a hardened synthetic rubber sufficient to withstand seismic stresses as well as stresses due to the opening and closing of the interrupter contacts within the device. In high voltage circuit breakers, the bushings for each phase are often mounted so that their ends have a greater spacing than their bases to avoid breakdown between the exposed conductive ends of the bushings.
The circuit breaker is comprised of three horizontal puffer interrupter assemblies enclosed in cylindrical tanks 15, 16, and 17. Current transformer assemblies 20 and 21 (referring to FIG. 2), which comprise one or more current transformers and their exterior housings, are located underneath the bushing insulators on the exterior of the breaker to facilitate their replacement in the field. Current transformers 20 and 21 measure the outgoing current.
FIG. 2 provides a side view of the three-pole circuit breaker of FIG. 1 that shows the corresponding exit bushing insulator, 13, of the interrupter assembly housed in tank 15. FIG. 2 illustrates how entrance bushing insulator 10 and exit bushing insulator 13 is associated with tank 15. The entrance and exit bushing insulators for the interrupters in tanks 16 and 17 (not shown in FIG. 2) are arranged in a similar fashion.
Referring to FIG. 1 and FIG. 2, the three interrupter tank assemblies are mounted on a common support frame 19. The operating mechanism that provides the necessary operating forces for opening and closing the interrupter contacts is contained within an operating mechanism housing or cabinet 18. The operating mechanism is typically mechanically coupled to each of the interrupter assemblies through a common linkage such as a drive cam. The operating mechanisms can be, but are not limited to, compressible springs, solenoids, hydraulic, or pneumatic-based mechanisms.
FIG. 3 is a partial, cross-sectional view of the interrupter assembly housed within cylindrical tank 15 and shown in FIG. 1 and FIG. 2. A typical circuit interrupter is comprised of stationary and movable contact assemblies 31 and 23, respectively. Entrance insulator bushing 10 houses a central conductor 22 which supports movable contact assembly 23 within conductive tank 24. Movable contact assembly 23 is affixed to an insulator tube 25 through which a linearly operating rod 26 extends. Rod 26 operates movable contact 27 between its open and closed position in a well-known fashion.
Exit insulator bushing 13 houses a central conductor 30 which is connected to the stationary contact assembly 31 and is also supported within conductive tank 24. An insulator tube 32 extends between the stationary contact assembly 31 and the movable contact assembly 23.
The interior volume of tank 24, as well as the entrance and exit insulating bushings 10 and 13, are preferably filled with an inert, electrically insulating gas such as SF6. The electrically insulating gas fulfills many purposes. The arcing contacts within both the stationary and movable contact assemblies are subject to arcing or corona discharge when they are opened or closed. Such arcing can cause the contacts to erode and disintegrate over time. Current interruption must occur at a zero current point of the current waveshape. This requires the interrupter medium to change from a good conducting medium to a good insulator or non-conducting medium to prevent current flow from continuing. Therefore, a known practice (used in a xe2x80x9cpufferxe2x80x9d interrupter) is to fill a cavity of the interrupter with an inert, electrically insulating gas that quenches the arc formed. During operation of the contacts in assemblies 23 and 31, a piston, which moves with the movable contact in assembly 23, compresses the gas and forces it the compressed gas between the separating contacts and toward the arc, thereby cooling and extinguishing it. The gas also acts as an insulator between conductive parts within housing 15 and the wall of tank 24.
Circuit breakers can switch various devices in an electric utility system. Primarily, these devices include transmission lines, transformers, shunt capacitor banks, and shunt reactors within an electrical substation, power distribution substation, or power transformer and distribution substation. The electrical substation converts the high voltage power carried by long-distance transmission lines into lower distribution voltage that services homes and businesses. FIG. 4 provides a top view of the circuit breaker of FIG. 1 as it is commonly installed within an exterior electrical substation. These substations generally cover a large surface area and are not aesthetically pleasing. Given their design, these substations require a great deal of maintenance due to their continuous exposure to climatic and seismic events.
As FIG. 4 shows, the conductive ends of the bushings are connected to a series of individual air disconnect switches or blades 40 that relate and connect each phase of the circuit breaker to the overhead, electrical substation bus (not shown in FIG. 4). Air disconnect switches 40, that relate to incoming and outgoing voltage, are each independently supported on electrically grounded frames. This arrangement requires electrical clearance on both sides of the circuit breaker to allow sufficient electrical isolation during maintenance and repair. In general, conventional disconnect switches are located on both sides of the breaker and are larger than the breaker. Thus, the disconnect switches occupy a larger surface area, or foot print, than the breaker itself. This arrangement may become impractical and unsafe if space in the electric utility system is limited. Moreover, more intensive maintenance and repair tasks, or a complete over-haul of the switching device, may be more difficult due to the limited real estate in the electric utility system.
The present invention fulfills these needs in the art by providing electrical switching devices that conserve real estate and reduce equipment within an electrical substation. In many instances, conventional breaker and disconnect switch assemblies occupy a surface area or footprint about three times greater than that of the present invention. The present invention also reduces maintenance and repair costs and time by facilitating access to the switching device and its sub-components.
According to the invention, the electrical switching device comprises a frame that supports a plurality of legs that terminate with wheels, one or more tanks that house the circuit interrupter assembly, and bushings. The bushings extend outwardly from the circuit interrupter tank and terminate with a conductive end. In preferred embodiments, the frame further comprises a locking device on the wheels and a winch. One or more disconnect switches connect the conductive ends of the bushings to incoming and outgoing power sources within the electrical system such as an overhead bus. In preferred embodiments, the disconnect switches are mounted onto the switching device rather than the substation power sources. The height of these disconnect switches, or the conductive ends of the bushing if the switches are mounted onto the bus, are staggered with respect to each other.
In preferred embodiments, a rail system or a pair of removable beams is used to translate the device from a first position to a second position for maintenance. The locking devices on the wheels of the switching device, such as foundation clamps in preferred embodiments, are disengaged to allow translation of the device from its fixed or first position. The wheels on the switching device engage the rails and the switching device is translated across the rails by a winch or other means to a second position. The distance between the first position and the second position is sufficient to provide adequate electrical clearance. In preferred embodiments, this distance is at least about 30 inches multiplied by a factor of 1, 2, 4, or 8 for 72 kV, 145 kV, 242 kV, or 362 kV devices, respectively. The staggered height of the disconnect switches or conductive ends of the bushings allow the device to translate from the first position and the second position without interference.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention as claimed. The accompanying drawings are included to provide a further understanding of the invention. In the drawings, like reference characters denote similar elements throughout several views. It is to be understood that various elements of the drawings are not intended to be drawn to scale.
A more complete understanding of the present invention, as well as further features and advantages of the invention such as its application to other electrical devices within a substation or system, will be apparent from the following Detailed Description and the accompanying drawings.